Ultra-high frequency ignition device



July 2, 1946. N. KORMAN ULTRA-HIGH FEQUENCY INITION DEVICE Filed Sept. 2, l943 4 7. J .WI f

I PatentedJly 2, 1946 UNITED STA'i' ES PATE NT OFFICE ULm-me FREQUENCY GNI'rIoN mz-:vc: y

Nathaniel I. Kuman, Camden, N. J., assi noto Radio Corporation o! America, a 'como'ationot Delaware Application September 2, 1943, Serial No. 501,01'

. 1 This invention relates generally to ignition systems for internal combus'tion engines and particularly to ignition plugs of the type in which a metallic element is raised to a sufliciently high temperature by electrica means to cause ignition.

Present ignition systems for aircraft use have the distinct disadvantage that considerable radio r interference is generated by the high potentials 'and eomparatively low frequencies involved.

Numerous ignition shielding devices' are known tor decreasing the inherent radio interference in said systems, but such devices have limited utility due to 'wide variations in moisture. pressure and temperature gradients encountered in radio aircrart operation. For example. when an airplane files through a cloud, considerable condensation may occur within the shielding surrounding the high tension spark plug leads, re-

, sulting in reduced emciency of the ignition system and obiectionable radio interference. Moreover, at low pressures experienced at extremely high altitudes, sparkover may occur in the ignipedance' coaxial transmission lines`or waveguides tion distribution system thereby 'causing engine faiiure. various methods, including the use of air -pumps, have been devised for exhausting the moisture or increasing the air pressure within the high tension electrostatic ignition shielding,

but the additional apparatus required added weight and has other serious disadvantages;

A further disadvantage of present ignition systems lies in the inherent 'unreliability' of spark plugs. The operation of spark plugs is hampered by the corrosion, erosion, and the accumulation of carbon deposits, and as a result a. large pereentage of airplane engine failures are caused by !ailure ot the spark plugs.

The instant invention is an improvement upon the system described in the copending'U. B. application oi' Francis X, Rettenmeyer ser. No. 5,046 filed May 29, 1942, entitled .Ultra-high i'requency ignition system. This copending application discloses and claims an ultra-high frequency ignition system which utilizes the' advantages oi' low inherent radiation from low impedance high frequency transmission lines or from wave 8 Claims. (Cl. 123-145) v erator, such as, for example; the type described 4 in the copending application mentioned heretofore, may be employed for deriving ignition power. i This power is transmitte'd by low imwhich interconnect the ignition g`enerator.and the ignition plugs. suitable impedance trans- .forming means are employed at both generator and plug to obtaineflicient transfer of power.

The present invention difiers from the type of plug described in the copending application mentioned heretofore in that substantially no sparking occurs in the ignition plug. The resistive element may be a relatively rigid metallc conductor providing a relatively high resistance at the operating ignition frequency. Since high frequency currents flow substantially only on the surface of a conductor, extremely high' temperatures on the conductive surface may be obtained in extremely short time intervals, and when the ultra-'high frequency energy is removed. the thermal capacity of the interior of the conductor 33 rapidly cools the extremely hot surface portions.

guides which couple an ultra-high frequency pulse i generato'r to tuned sparking devices which -comi prise quarter wave sections of concentric transmission line. The system thus described., by utilizing ignition voltages oi' ultra-high frequency considerably above the normalfrequencies used Among the object: of the invention are to provide an improved ultra-high frequency ignition plug. Another object of the invention is to provide an improved ultra-high frequency ignition plug wherein ultra-high frequency energy is utilized to heat a resistive element disposed within the combustion chamber. A further object of the invention is to provide an improved ultra-high frequency ignition plug wherein ultra-high' trequency energy derived from a low impedance concentric transmissi'on line is applied to a con-` centric line forming 'the plug which provides voltage transformation to derive relatively high ignition currents which may be applied' to a resistive element connectedbetween the high currenttermin'als of the-concentric line pl g. An-

` other object oi' the inventionis to provide an for radio transmission, and byemploying low impedance ignition energy transmission lines.

greatly reduces radio interterenoe and provides improved ultra-high' frequency ignition -plug comprising a concentric transmissi'on line having alength oi' the orderoi an even multiple of one ment. Another object of 'the invention is to pro- 'vide an improved ultra-high frequency ignition plug having plug connection means for terminating a coaxial ignition trans'mission line. A further object is to provide an ignition plug i having a resistive heating element' comprising a thin metallic' film deposited upon an insulating refractory material. V

The invention will-be further dacribed by reference to the accompanying drawing of which' Figure 1' is a cross-sectional elevational view of one embodiment thereof, Figure 2 is a ,cross-sectional elevational view of a second embodiment thereof, and Figura 3 is'a fragmentary cross-sec tional view of a modification of the devices of Figs. 1 and 2. Similar reference charactersare applied to similar elements throughout the drawing.

Referring to Figure 1, the ignition plug comprise an outer cylindrica conductor l coaxial with and substantially surrounding an inner conductor 2.' The resultant coaxial transmission line section is open-circuited at one end but effecv tively sealed by an insulating gas tight plug 3. A circular or rectangular opening 4 in the outer cylindrical conductor I includes an insulating 'plug 5 which effectivelyseals the opening and ,supports a second internal conductor 6 which passes therethrough. One end of the second ina -ternal conductor 6 is terminated at a selected point on the first internal conductor 2 while the other endis terminated 'adjacent the open end of a conductive sleeve 'I which projects from the aperture- 4 normal to the outer, cylindrical conductor. I. The second internal conductor 6 and the conductive sleeve 'I are' formed to receive and terminate a low impedan'ceconcentric ignition transmission line 8 which includes an outer conductor a and an inner 'conductor o, the iatter terminating in a suitable contact clip ll for engaging the second inner conductor 6. The low impedance ignition transmission line is connected to any suitable source of ultra-high frequency ignition energy. 4

The outer cylindricalconductor l includes a threaded sleeve !2 adapted to engage the conventional threaded spark plug port. The threaded plug sleeve l2 may include 'a fiattened portion 13 adapted to provide suitable surfaces for engagem'ent with a spark plugwrench. The ends of the coaxiai conductors I and 2 extending into sistive element H.

As explained heretofore, the connection of the v second inner conductor 6 to the first inner conf the combustion chamber are terminated in a recombustion chamber. The element also should have suilicient mass to provide ample h'eat capacity for quickly reducing surface temperature during the intervals between ignition energy pulses.

The relative dimensions of the ignition plug and the point of connection between the second internal conductor 6 and the first internal conductor 2 will depend upon the ignition frequencies employed and upon thevoltage transformation deslred,'since it should be understood that standing waves will be establish'ed intermediate the conductors l, 2.

The essential difference between Figures l and pact ignition plug since the portion remote from the resistive element ll may be considerably shorter while still providing standing waves along the inner ,conductor 2.

The resistive element II, 'employedin ,either of the embodiments of the invention described in Figs. 1 and 2, may comprise a thin metal film IS deposited by sputtering or by chemical means on some insulating refractory material ll such as glass, quartz or ceraniic, as illustrated in Figure 3.

The ignition energy may be in the form of either short radio frequency or unidirectional current pulses. Voltage transformation between the low impedance 'transmission line and the resistive element may be accomplished as described heretoiore or in any other manner known in the art. Furthermore, the transmission lines interconnecting the ignition voltage 'source and the .ignition plugs may comprise either concentric ment comprises a relativeiy thin metallic film,

and wherein said last mentioned means comprises a refractory materia supporting aid film.

3. A tuned ignition device for ultra-high fre- ,quency 'ignition energy including an elongated -center electrode, a coaially disposed outer -eiectrode surrounding said center electrode and forming a concentric line section therewith', resistivemeans providing an ignition element connectlng c'ne end of said center -electrode to the proximate end of said outer electrode, and connecting means for said ultra-high frequency energy' connected intermediate the ends of said center electrode and to said outer electrode. v

4. A tuned ignition device for center electrode, a coaxially disposed outer elecultra-high frequency ignition energy including an elongated trode surrounding said center electrode and form ing a concentric line section therewith, resistive `means providing an ignition element connecting one end of said center electrode to the proximate end oi' said outer electrode, means connecting together the remaining proximate ends of said center and said outer electrodes and connecting means for said ultra-high frequency energy connected intermediatethe ends of said center elec-' trode and to said outer electrode.

5. Apparatus ot the type describedin claim 3.

connecting said connecting means to an ignition energy transmission line, and characterized by the fact that said connection to said center electrode provides eflective imped'ance matchingbetween seid transmission line and said ignition element.

' 6. Apparatus of the type' described in claimi including externally separable contact means for jcomplementery device.

6 v v including extemally seperable contact means i'or connecting said connectingv means to 'an ignition energy transmission line, and characterized by the :act that said connection to said center electrode provides eflective lmpedance matching between; said transmission line and said ignition: element.

7. A resonant isnitlon device-for ultra-high frequency ignition energy including anjelongated center lectrode equivalent substantially. to some odd multiple of one qum-ter wavelength of said 'energy and a resistive ignition element {termi- NATHANIELV I. KORMAVN.

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